Electrical measuring instrument



Jan. 31, 1961 LENEHAN 2,970,268

ELECTRICAL MEASURING INSTRUMENT Filed June 20, 1957 5 Sheets-Sheet 1 Jan. 31, 1961 B. E. LENEHAN 2,970,268

ELECTRICAL MEASURING INSTRUMENT Filed June 20, 195"! 5 Sheets-Sheet 2 Fig.2.

WITNESSES INVENTOR 2 Bernard E. Lenehun w 4 @we M ATTORNEY Jan. 31, 1961 B. E. LENEHAN 2,970,268

ELECTRICAL MEASURING INSTRUMENT Filed June 20, 1957 5 Sheets-Sheet I5 Jan. 31, 1961 LENEHAN 2,970,268

ELECTRICAL MEASURING INSTRUMENT 5 Sheets-Sheet 4 Filed June 20, 1.957

Jan. 31, 1961 B. E. LENEHAN 2,970,268

ELECTRICAL MEASURING INSTRUMENT Filed June 20, 1957 5 Sheets-Sheet 5 Fig.8.

2,970,268 ELECTRICAL MEASURING INSTRUMENT B ernard E. Lenehan, Bloomfield, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed June 20, 1957, Ser. No. 666,958

2 Claims. (Cl. 324-147) This invention relates to electrical measuring instruments and has particular relation to electrical measuring instruments of the moving iron type.

A moving iron instrument heretofore constructed includes a winding for producing when energized a mag netic field. One or more fixed magnetic elements of cylindrical configuration are disposed in the magnetic field produced by current flowing in the winding. A moving magnetic element is positioned in the magnetic field spaced from the axis of the fixed elements. When these magnetic elements are magnetized they develop attraction or repulsion forces therebetween. The moving element is mounted for rotation about the axis of the fixed elements with respect to the fixed elements under the influence of these forces.

Among the problems presented in the design of such an instrument is the elimination of undesirable forces developed between the magnetic elements in response to energization of the winding which cause an objectionable vibration of the moving element. It has been observed in such instruments that when the fixed elements are spaced from their axis by a distance different from that of the moving element forces are developed between the magnetic elements in response to energization of the winding by an alternating quantity which tend to cause vibration of the moving element in directions radially of the axis of rotation of the moving element. These undesirable forces are particularly noticeable when the moving element is adjacent a position corresponding to a full scale position.-

According to the invention a moving iron instrument is provided wherein the fixed and moving magnetic elements are arranged relative to one another such that the above-described undesirable forces are substantially eliminated. In a preferred embodiment of the invention the instrument includes a winding effective when energized for producing a magnetic field. The winding is carried by a tubular support to surround a central cavity of the support. A pair of cylindrical attraction magnetic elements and a cylindrical repulsion magnetic element are fixed within the opening of the support spaced along their common axis with the repulsion element intermediate the attraction elements. A moving magnetic element is spaced from this common axis adjacent the repulsion element for rotation relative to the fixed elements about the common axis.

In order to eliminate the above-referred to undesirable forces the invention provides that the attraction elements and the moving element are spaced from the axis of the attraction elements by substantially the same distance. With such arrangement forces developed between the attraction elements and the moving element which tend to cause vibration of the moving elements in directions radially of the axis are substantially eliminated.

In order to improve the efiiciency of the instrument a pair of magnetic members preferably of cup-shaped configuration are mounted by the support adjacent the attraction elements with flanges of the cup-shaped members 10- 2,979,268 Patented Jan. 3.1, 1961 cated within recesses of the ends of the support. In order to provide efiective shielding of the instrument against stray magnetic fields a continuous magnetic shield is positioned to surround the support and the winding carried thereby. With the magnetic shield and the cupshaped members in operative positions, portions of the support extend between the shield and cup-shaped members to effect a uniform spacing between the shield and cup-shaped members. The shield and cup-shaped members are further positioned with respect to each other such that the shield and flanges of the cup-shaped members overlap to provide a closely coupled magnetic circuit.

The cup-shaped members may conveniently serve to support the attraction elements in operative positions. Forthis purpose the invention provides an attraction element which is integrally connected to a cup-shaped magnetic member. The attraction element is conveniently formed by drawing material of the base of the cup-shaped member through an opening of the base.

The instrument further includes a pair of frame members which are arranged to mount the support together with the cup-shaped members and magnetic shield. The frame members are arranged such that a concentric mounting of the support with respect to the axis of rotation of the moving element is assured. These frame members also carry bearing means for supporting the moving element for rotation.

it is, therefore, an object of the invention to provide an improved electrical instrument of the moving iron type.

It is a further object of the invention to provide a moving iron electrical instrument having an improved arrangement of the operating parts of the instrument.

It. is a still further object of the invention to provide a moving iron electrical instrument having fixed and moving magnetic elements arranged with respect to one another such that undesirable forces developed between the elements in response to energization of the instrument are substantially eliminated.

Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic view in perspective illustrating a moving iron electrical instrument;

Fig. 2 is a view in elevation with parts shown in section illustrating details of construction of the instrument of Fig. 1;

Fig. 3 is a view in top plan of a magnetic member of the instrument of Fig. 2;

Fig. 4 is a view in cross section of the member of Fig. 3; l

Fig. 5 is a view in the top plan of'a support and additional magnetic part of the instrument of Fig. 2 with parts broken away;

Fig. 6 i s a view in bottom plan of a frame member of the instrument of Fig. 2;

Fig. 7 is a view in top plan of another frame member of the instrument of Fig. 2; and

Fig. 8 is a view in elevation with parts shown in section and with parts broken away illustrating a further aspect of the invention.

Referring to the drawings there is schematically illustrated in Fig. 1 portions of an electrical instrument of the moving iron type constructed in accordance with the invention. The instrument of Fig. l is represented generally by the numeral 1 and has a stator assembly which includes an electroconductive winding 3 having an axial opening. When the winding 3 is energized b'ycurrent flowing therethrough a magnetic field is established in the opening of the winding. For example, when current flows in the winding 3 in the direction of the arrow 4 a magnetic flux is established which flows through the p n f e W ndi g i th di e e of th arro 5 observed to be positioned between the elements 6 and 9 in reversed relation with respect to the elements 6 and 9 such that the wide end of the element 7 is adjacent the narrow ends of the elements 6 and 9. It is noted that these fixed elements are positioned within the opening of the winding 3 spaced along their common axis so as to be in the path of magnetic flux produced by current flowing in the winding 3. The elements 6 and 9 may be termed attraction elements whereas the element 7 is referred to as a repulsion element.

When the winding 3 is energized magnetic flux produced by the winding traverses the fixed magnetic elements to induce magnetic poles therein. For the direction of current in the winding 3 as represented by the arrow 4 magnetic poles are induced in the fixed elements having polarities as shown in Fig. 1. As viewed in Fig. 1 the upper portions of the fixed elements have north magnetic poles induced therein whereas the lower portions of the fixed elements have south magnetic poles induced therein.

The instrument 1 further includes a rotor assembly 9 which comprises a moving magnetic element 11 which may be constructed of soft iron in the manner of the fixed magnetic elements. The moving element 11 is positioned within the opening of the winding 3 spaced from the axis of the fixed elements adjacent the fixed element 7. It is noted that for magnetic flux flowing through the opening of the winding in the direction of the arrow 5 the upper end of the element 11 as viewed in Fig. 1 has induced therein a north magnetic pole with the lower end of the moving element having induced therein a south magnetic pole. With this arrangement the moving element 11 will be repulsed by the fixed element 7 in a clockwise direction as viewed from the top of Fig. 1. In addition, the moving element will be attracted by the fixed elements 6 and 9 in a clockwise direction. By reason of the tapered construction of the fixed elements the repulsion forces between the elements 7 and 11 will decrease as the element 11 moves in the clockwise direction whereas the attraction forces between the elements 6, 9 and 11 will increase as the element 11 moves in the clockwise direction. Such tapered construction of the fixed elements provides a substantially linear response of the instrument.

The moving element 11 is conveniently mounted for rotation relative to the fixed elements 6, 7 and 9 about the axis of the elements 6, 7 and 9 by means of a shaft 13. The shaft 13 has afiixed thereto a suitable pointer 15 which traverses a suitably calibrated scale 17 in response to energzation of the winding 3. The element 11 occupies its full scale position when it is adjacent the wide ends of the elements 6 and 9. A suitable coil spring 19 is secured between the shaft 13 and the stator assembly to oppose rotation of the shaft.

Instruments of previous design have included magnetic elements similar in configuration to the elements 6, 7, 9 and 11. These elements have heretofore been arranged such that the fixed elements are spaced a greater distance from the axis of rotation of the moving element than the moving element. Wheninstruments of such previous type are energized by alternating quantities it has been observed that forces are developed between the fixed and moving elements which tend to cause vibration of the moving element in directions radially of the axis of rotation of the moving element. These forces are most noticeable when the moving element is adjacent a position corresponding to a full scale position. For this position of the moving element the forces developed between the attraction elements and the moving clement have maximum values. Certain of these forces act in directions radially of the axis of rotation to thereby produce objectionable radial vibrations of the moving element.

When the winding 3 is energized by a direct quantity it is observed that forces are developed between the fixed and moving elements which tend to shift the shaft 13 radially from its proper position. This action is also objectionable.

In accordance with the present invention the fixed and moving magnetic elements are arranged relative to one another such that forces developed between these elements which act radially of the axis of rotation of the moving element are substantially eliminated. To this end the invention provides that the attraction elements 6 and 9 and the moving element 11 be proportioned and arranged such that these elements "are spaced substantially equal distances from the axis of the shaft 13. Stated in other words the elements 6 and 9 are arranged so that they lie in the axial projection of the surface of revolution generated by movement of the element 11 about the axis of the shaft 13.

With such arrangement the forces developed between the fixed and moving element in response to energization of the winding 3 are located in substantially a cylindrical plane which is concentric about the axis of the shaft 13. Due to the shaping of the fixed and moving elements these forces have a line of action which is inclined relative to the axis of the shaft 13.

Referring now to Fig. 2 there is illustrated the instrument 1 constructed in accordance with the teachings of the present invention. As there shown a suitable support 21 is provided for supporting certain of the operating parts of the instrument 1. The support 21 is preferably constructed of a suitable electrical insulating material. As shown in Figs. 2 and 5, the support 21 is of tubular configuration including an annular recess 23 of the side wall of the support proportioned to receive the winding 3. The support 21 further includes a central cavity 25 which extends entirely therethrough to open at the ends of the support. The cavity 25 is shown in Fig. 5 as being of circular configuration. The upper end of the support 21 as viewed in Fig. 2 is formed with a recess 27 which defines an annular peripheral wall portion 29 and a raised central portion 30. In a similar manner the lower end of the support 21 as viewed in Fig. 2 is provided with a recess 31 to define an annular peripheral wall portion 33 and a raised central portion 34.

In order to improve the efficiency of the instrument 1 a pair of similar magnetic members 35 and 37 are positioned respectively adjacent the upper end and lower ends of the support 21 as viewed in Fig. 2. The mem bers 35 and 37 may be formed of any suitable soft magnetic material and are illustrated as being of cup-shaped configuration. Since the members 35 and 37 are of similar construction only the member 35 is shown in detail. The member 35 is illustrated in detail in Figs. 3 and 4 as comprising a flat base portion 39 having an annular flange 41. The base portion 39 includes a central opening 43 with a diameter substantially equal to the diameter of the cavity 25 of the support 21. A plurality of portions 45 are struck down from the base portion 39 to extend through the opening 43. As shown in Figs. 2 the member 37 similarly includes a base portion 47 with a flange 49 and an opening 51 of the base portion with portions (not shown) of the base portion struck down to extend through the opening 51.

The members 35 and 37 are mounted by the support 21 in the manner illustrated in Fig. 2. As there shown, the member 35 is positioned with the flange 41 within the recess 27 of the support 21 in engagement with the annular wall 29. With the arrangement the base'portion 39 engages the upper end surface of the support 21 with the opening 43 aligned with the cavity 25 to have the flange 41 projecting in a downward direction as viewed in Fig. 2. In a similar manner, the member 37 is positioned with the flange 49 within the recess 31 of the support 21 in engagement with the wall 33. The base portion 47 engages the lower end surface of the support as viewed in Fig. 2 with the opening 51 in alignment with the cavity 25 to have the flange 49 projecting toward the flange 41 of the member 35.

The elements 6 and 9 may be mounted within the cavity 25 of the support 21 in any suitable manner. In order to permit adjustment of the elements 6 and 9 about the axis of the shaft 13 to provide a desired scale distribution the elements 6 and 9 are conveniently supported within the cavity 25 by means of the magnetic members 35 and 37. For this purpose, the element 6 is positioned within the opening 43 of the member 35 as shown in Figs. 3 and 4 such that the struck down portions 45 engage the outer surface of the element 6. The element 6 may be secured in this position in any suitable manner such as by solder or cement which may be positioned between the element 6 and the portions 45. The element 6 may be Welded to the member 35 if desired. The element 9 may be secured to the member 37 in a similar manner. With this arrangement adjustment of the elements 6 and 9 is conveniently effected by adjusting the members 35 and 37 about the axis of the shaft 13. Such adjustment of the members 35 and 37 may be accomplished in any suitable manner.

Referring now to Fig. 8 there is illustrated an instrument including parts of different construction than parts of the instrument of Fig. 2. Parts illustrated in Fig. 8 which are similar to parts of Fig. 2 are represented by the same reference numerals.

According to thepresent invention the instrument of Fig. 8 includes magnetic parts of improved construction.

As there shown the invention provides an upper magnetic member 52 having integrally connected portions 54 and 56 and a lower magnetic member 58 having integral portions 60 and 62. It is noted that the portions 56 and 62 constitute attraction elements similar to the elements 6 and 9 of Fig. 2. The portions 54 and 60 constitute cup-shaped members similar to the members 35 and 37 of Fig. 2. The portions 56 and 62 are formed by drawing material from the bases of the members 52 and 58 through suitable openings of these bases. It is observed that the members 52 and 58 are positioned such that their flanges extend in opposing directions.

In order to position the members 52 and 58 in the manner shown in Fig. 8 the configuration of the support 21 of Fig. 8 is modified from the configuration thereof shown in Fig. 2. This modification involves a reduction in the height of the raised central portions 30 and 34 of the support.

In order to provide effective shielding for the instrument 1 against stray magnetic fields a magnetic shield 53 is provided having the configuration illustrated in Figs. 2 and 8. As there shown, the shield 53 is of tubular construction having a continuous peripheral wall. The shield 53 may be constructed of any suitable material such as soft iron. The shield 53 is positioned as shown in Figs.'2 and 8 to surround the support 21 in engagement with the side wall of the support. The shield may be secured to the support in an operative position in any suitable manner. It is observed with reference to Fig. 2 that the axial length of the shield is selected such that the shield 53 surrounds the winding 3, the magnetic elements 6, 7, 9 and 11 and the flanges 41 and 49 of the magnetic members 35 and 37. The

axial length of the shield is slightly less than the overall axial length of the support 21.

With the arrangement described the wall 29 ofthe support 21. extends between and engages the shield 53 and the flange 410i the member 35. 'In a similar manner, the wall 33 extends between and engages the shield 53 and the flange 49 of the member 47; This arrangement provides a uniform spacing of the shield 53 and the members 35 and 37 in directions transverse to the shaft 13 for each instrument regardless of variations in dimensions of the parts. It is further noted that the shield 53 extends beyond the edges of the flanges 41 and 49 so as to overlap these flanges in a direction parallel to the direction of extension of the shaft 13. This construction provides a closely coupled magnetic circuit for the instrument 1 to thereby provide an instrument of improved sensitivity to energizing quantities.

The shield 53 may also be employed in the instrument shown in Fig. 8. members 52 and 58 are spaced fromthe shield 53 by the Walls 29 and 33 in the manner of the instrument of Fig. 2.

In order to support the previously described parts of the instruments in operative positions a frame assembly is provided which may include a pair of frame members 55 and 57 which are positioned respectively at the upper and lower ends of'the support 21 as viewed in Fig. 2.

Details of construction of the frame member 57 are best shown in Fig. 7. As there shown the member 57 comprises a base portion 58 including a central projection 59 having a threaded opening 61 proportioned to receive a suitable threaded bearing screw 63 shown in Fig. 2. The projection 59 is connected to the base portion 58 by a plurality of spaced connecting parts 65, 67 and 69.

The base portion 58 of the member 57 is provided with a pair of annular stepped grooves 73 and 75 which are arranged concentrically with respect to the opening 61.

The grooves 73 and 75 are provided for the purpose of receiving respectively end portions of the wall 33 of the support 21 and the shield 53. This arrangement assures a concentric mounting of the support 21 and the shield 53 with respect to the shaft 13. Each of the connecting parts 65, 67 and 69 includes an integral leg portion with the leg portions 76 and 77 of the connecting parts 65 and 67 respectively being illustrated in Fig. 2. When the member 57 is operatively positioned with respect to the support and its associated parts the projection 59 extends through the opening 51 of the member 37 into the cavity 25 of the support.

'As bestshown in Fig. 6 the frame member 55 includes a base portion 78 with a projection 79 extending therefrom having a threaded opening 81 proportioned for receiving a suitable threaded bearing screw 83 shown in Fig. 2. In order to mount the support 21 and the shield 53 the base portion 78 of the member 55 is formed with a pair of stepped annular grooves 85 and 87 for receiving respectively end portions of the wall 29 of the support 21 and the shield 53. The grooves 85 and 87 are spaced from the opening 81 of the member 55 by the same distance by which the grooves 73 and 75 are spaced from the opening 61 of the member 57. The grooves 85 and 87 are further positioned concentrically with respect to the opening 81. This arrangement assures a concentric mounting of the support 21 and its associated parts by the frame members with respect to the shaft 13 which is also supported by the frame members.

In order to permit securement of the support 21 to the frame member 55 the member 55 includes a plurality of projections of the base portion 78 each having a threaded opening 89 as shown in Fig. 6. These openings 89 are positioned in alignment with suitable threaded openings 91 of the adjacent end surface of the support 21 when the support 21 and member 55 are operably positioned with respect to each other. In order to secure the support 21 to the member 55 suitable screws 93 may be passed through the aligned openings 89 and 91. The screws 93 pass through suitable openings 95 of the base portion 39 of the magnetic member 35 shown in Fig. 3. The openings 95 are somewhat elongated to permit lim- It is noted that the flanges of the 7 ited adjustment of the member 35 about the shaft 13 in the manner previously described without interference from the'se'f'ews 93.

In orderto secure the cup-shaped member 35 to the support 21 suitable screws 97 are passed through openings 99 of the base portion 39 of the member 35 into suitably threaded openings 101 of the adjacent end surface of the support 21. The openings 99 of the member 35 are elongated to permit adjustment of the member 35 about the shaft 13. The cup-shaped member 37 is similarly secured to the support 21 by passing screws 103 through openings 105 and 107 which are formed respectively in the base portion 47 of the member 37 and in the adjacent end surface of the support 21.

In order to provide a rigid structure the frame members 55 and 57 are secured together in the manner illustrated in Fig. 2. As there shown a plurality of studs 109 are passed through openings 111 of the frame member 55 and openings 113 of the leg portions of the frame member 57. Suitable nuts 115 engage the threaded ends of the studs 109 to effect the securing action. The studs 109 may extend into a suitable base member 117.

Although the invention has been described with reference to certain specific embodiments thereof numerous modifications are possible and it is intended to cover all modifications falling within the spirit and scope of the invention.

I claim as my invention:

1. in an electrical instrument, a winding, a pair of attraction magnetic elements each of arcuate configuration, said attraction elements each being positioned arcuate about an axis in the path of magnetic flux established by current flowing in the Winding, said attraction elements being spaced along said axis, a magnetic part spaced from said axis positioned in the space between said attraction elements in the path of said magnetic dim, and means mounting said magnetic part for rotation about saidaxis relative to said attraction elements in response to forces developed betweensaid attraction elements and said magnetic part by said magnetic flux, said attraction elements and magnetic part being arranged such that a line .whichextends parallel to said axisintersectssaid attraction elements and magnetic partat each position of the magnetic part in its path of travel,

2. In an electrical instrument, a winding, apair of attraction magnetic elements eachof arcuate configuration, said attraction elements each being positioned arcuate about an axis in the path of magnetic flux established by current flowing in the winding, said attraction elementsbeing spaced along said axis, a magnetic part spaced from said axis positioned in the space between said attraction elements in the path of said magnetic flux, a repulsion magnetic element of arcuate configuration positioned. arcuate about said axis in the path of said magnetic flux to surround said magnetic part, and means mounting said magnetic part for rotation about said axis relative to said elements in response to forces developed between said elements and said magnetic part by said magnetic flux, said attraction elements and magnetic part being arranged such that a line which extends parallel to said axis intersects said attraction elements and magnetic part at each position of the magnetic part in its path of travel.

References Cited in the file of this patent UNITED STATES i ATEN'rs 1,501,189 Record i s 1T5, 1924 2,183,566 Hoare V pea 19 1939 2,610,989 Wiese et al. Sept. 16, 1952 2,865,001 Millar Dec. 16, 1958 FOREIGN PATENTS 350,380- Great Britain time '1, 1931 

